Brachytherapy is a form of cancer treatment in which a radioactive energy source is placed into or adjacent to a malignant tumor. Generally, brachytherapy can be divided into two categories: high dose rate (HDR); and low dose rate (LDR). In HDR brachytherapy, a radioactive energy source with high activity is placed into or adjacent to the malignant tumor for a predefined period of time. Conversely, LDR brachytherapy entails the placement of a low activity radioactive energy source into or adjacent to the malignant tumor for an indeterminate period of time.
In LDR brachytherapy, radioactive isotopes are used as the radioactive energy sources. Some of the more common radioactive isotopes used in LDR brachytherapy include Iodine-125, Palladium-103, Gold-198, Ytterbium-169, and Iridium-192. These isotopes are typically packaged in a housing constructed of a lightweight and durable material, such as titanium, and are commonly referred to as isotope seeds. The dimensions of the isotope seeds can be extremely variable both in diameter and in length. The radioactive isotopes commonly used in LDR brachytherapy are selected for their low energy and relatively short half-life. Low energy sources provide for a limited tissue penetration by the emitted radiation, so that the radiation's effects are limited to the tumor without substantially affecting adjacent normal tissue. A short half-life is advantageous in that the dose of radiation that is delivered depletes in a reasonably short period of time.
The area of therapeutic effect for Iodine-125 and Palladium-103 is limited to a sphere approximately 1 cm in diameter around the isotope seed. As a result, a three-dimensional array of isotope seeds is commonly used to treat a tumor. In LDR brachytherapy of prostate cancer, a multitude of isotope seeds is typically used. Since solid tumors, like those found in prostate cancer, are perceived to be diffuse, the entire organ is targeted for therapy.
In order to place isotope seeds into the aforementioned three-dimensional array, needles, using a two-dimensional grid pattern in conjunction with longitudinal spacing, can deliver isotope seeds. The two dimensional grid is frequently defined by a needle guide, called a template. The template is provided with a plurality of holes that provide guidance for the longitudinal progression of the needles, thus insuring their desired two-dimensional position within the tumor. After the two-dimensional needle array is positioned within the tumor, the isotope seeds are deposited along the longitudinal axis of each needle.
Proper spacing of the isotope seeds along the longitudinal axis of the needle is accomplished through the use of biocompatible spacers further deposited between the isotope seeds. The use of spacers also serves to maintain the low energy effect on the prostate by maintaining a distance between the isotope seeds. The spacers and isotope seeds are alternately loaded into the needle prior to placement of the needle into the tumor. Upon placing the needle into the tumor, a cannula is engaged to maintain the position of the line of isotope seeds and spacers as the needle is withdrawn. This yields a line of isotope seeds in their proper longitudinal position. This process is repeated at the other two dimensional grid coordinates, thus forming the desired three dimensional array of isotope seeds.
An improved version of this procedure, as disclosed in U.S. Pat. No. 6,213,932, includes transparent plastic seed cartridges, detachably connected to the applicator, for holding a plurality of radioactive isotope seeds. This version enabled a surgeon to visually ascertain the number of spacers within a cartridge, thereby eliminating the guesswork previously involved in determining the number of remaining isotope seeds, greatly reducing the time required to load a needle.
A device that includes a cartridge having a plurality of individual isotope seeds, known as the Mick™ applicator system, registered to Mick Radio-Nuclear Instruments, Inc., is currently in widespread use. The cartridge retains a large number of individual isotope seeds that have been loaded therein at a separate facility. Additionally, isotope seeds can also be loaded into the cartridge at the hospital or at a nuclear pharmacy, thereby eliminating the time and cost requirements of loading individual isotope seeds in an operating room.
In the prior art, a seed-containing cartridge is attached to an applicator in a manner substantially similar to the way a magazine is attached to a firearm. The cartridge is spring-loaded to force one isotope seed at a time into a seed discharge chamber that further retains a single isotope seed for insertion into a needle. A special hollow needle is connected to the needle holder of a distal end of the applicator. A push rod is inserted into a distal end of the applicator and pushed directionally in a proximal-to-distal direction. The distal end of the push rod engages an isotope seed in the seed discharge chamber and drives the isotope seed into the hollow interior of the special needle and then out of the distal end of the needle into the prostate. The surgeon then extracts the needle to a predetermined distance, withdraws the plunger rod to a position on the proximal end of the seed discharge chamber so that an additional isotope seed can enter the chamber from the cartridge. Subsequent isotope seeds are then introduced into the needle, and then prostate, in an identical manner.
Although the Mick™ applicator system eliminates the risk of dropping individual isotope seeds in an operating room, it increases the amount of time required to implant a multitude of isotope seeds into the prostate because of the inability to inject more than one seed at a time. Further advances in this technique have additionally resulted in a reduction of the guesswork required by the surgical staff to determine the number of isotope seeds in a cartridge. However, these systems do not provide for either an identical loading system for spacers or for a system for visualizing the order of isotope seeds and spacers to be loaded into a needle.
Thus, there is a need for an improved applicator system that semi-automatically and sequentially loads radioactive isotope seeds and biocompatible spacers and that enables a surgeon to visually ascertain the number and sequence of isotope seeds and spacers within a cartridge.